1. Field of the Invention
This invention relates to the field of optical communications, and in particular to a method of aligning optical waveguides.
2. Description of Related Art
Optical waveguides, which typically consist of a core layer surrounded by a cladding layer, are used extensively in modern telecommunications as a transport medium. There is a need to be able to quickly and cheaply, yet accurately and reliably, align waveguides so that high performance interconnects can be made. Typically, in order to properly align two single-mode telecom fibers, sub-micron accuracy in three translational dimensions is required, as well as fiber tilt correction for non-coaxial fiber axes. Any technique used must be easy to perform and capable of automation.
There are many ways of making optical interconnects. One technique is based on optimizing the optical transmission through the two waveguides. U.S. Pat. No. 4,325,607 discloses the use of special sleeves. S. Berglund, 31′ Annual Connector and Interconnection Symposium, Waretown, N.J., USA, pp183-198, 1998 suggests the use of precision ferrules and V-grooves as alignment guides. U.S. Pat. Nos. 5,511,138 and 5,633,968 disclose the use of interlocking guiding pins outside the waveguide structure.
The making of an optical connection based upon optimizing light throughput is laborious as light has to be coupled into one of the waveguides and the light transmission measured through the connected guide. In the case of polarization maintaining fibers raw transmission optimization is not a sufficiently accurate alignment technique to preserve a high degree of polarization.
The use of special sleeves and ferrules requires precision manufacturing and is sensitive to variations in fiber diameter and/or core offset.
V-grooves can be used to align fibers to arrays of microfabricated waveguides, but they must be made with tight tolerances so that there is no drift in alignment across an array. V-grooves are also sensitive to variations in fiber diameter and core offset as well as to debris which can collect in the grooves.
The use of interlocking pins fabricated on a structure which supports the waveguides but is outside the waveguide's core and cladding as disclosed in U.S. Pat. Nos. 5,511,138 and 5,633,968 requires extremely high accuracy for the insertion of pins into receptacles, especially for an array of waveguides which can span a greater distance than a single guide. Again this technique is also sensitive to variations in fiber diameter and core offset.
U.S. Pat. No. 3,883,353 describes the use of a photolithographic process to create a protrusion on one fiber core which can be inserted into a photolithographically produced receptacle on a second fiber core to connect two single-mode fibers. The construction process as described in this patent involves coating the fibers with a light sensitive material, such as a photoresist, exposing the photoresist to Ultra Violet (UV) light in the core region by coupling light into the fibers, developing the resists, chemically etching the exposed regions, and finally removing the resist masks. The main drawback of this approach is the use of a complicated time consuming procedure to create the protrusion and receptacle parts. The inventors also point out that a serious drawback with their approach is that the UV can expose a wider region than just the core, which reduces the accuracy and reliability of the technique. Furthermore, this patent does not describe how to align the protrusion and receptacle parts.